Synthesis of phthalocyaninatocobalt(II) and complex formation with imidazole

Two kinds of phthalocyaninatocobalt(II) with different substituents have been synthesized. Complexation of imidazole was observed to proceed in two steps to form a mono- and, subsequently, a di-imidazole complex in solution. It is thought that the steric effect of the substituents on the ring, control the number of coordinated imidazole molecules. The stoichiometry of the complexes was determined by Jobʹs titration method and the formation constants were then evaluated. The absorption spectrum of phthalocyaninatocobalt(II) exhibits a very broad band in thin films due to molecular aggregation while its di-imidazole adduct showed a sharp and red-shifted absorption band which is critical for optical recording materials.